Miscellaneous Methods in System
This section describes some of the methods in System
that aren't covered in the previous sections.
The arrayCopy
method efficiently copies data between arrays. For more information, refer to Arrays in the Language Basics lesson.
The currentTimeMillis
and nanoTime
methods are useful for measuring time intervals during execution of an application. To measure a time interval in milliseconds, invoke currentTimeMillis
twice, at the beginning and end of the interval, and subtract the first value returned from the second. Similarly, invoking nanoTime
twice measures an interval in nanoseconds.
Note: The accuracy of both
currentTimeMillis
and
nanoTime
is limited by the time services provided by the operating system. Do not assume that
currentTimeMillis
is accurate to the nearest millisecond or that
nanoTime
is accurate to the nearest nanosecond. Also, neither
currentTimeMillis
nor
nanoTime
should be used to determine the current time. Use a high-level method, such as
java.util.Calendar.getInstance
.
The exit
method causes the Java virtual machine to shut down, with an integer exit status specified by the argument. The exit status is available to the process that launched the application. By convention, an exit status of 0
indicates normal termination of the application, while any other value is an error code.